Exchange online forwarding

Question

Hi all,
I have a problem with email forwarding and I hope for your help.

Example:
myFirstAccount@example1.com --> is the mail mailbox that forwards the email to mySecondAccount@example2.com
mySecondAccount@example2.com --> is the mailbox that receives the email forwarded from the first mailbox
customer@example3.com --> is my customer's mailbox

If customer@example3.com sends an email to myFirstAccount@example1.com and mySecondAccount@example2.com is temporarily out of order, my customer receives a message from microsoftexchange@mydomain.onmicrosoft.com with the error "Delivery failed for the following recipients or groups: mySecondAccount@example2.com".

I don't want my customer to know that I'm forwarding my email to my second account.

Is possible to avoid this behavior?

Thank you for your help.
AS

Answer 1

Hi @Alain Sorrentini
Ok, thats a different the issue. You are forwarding and that breaks all the SPF/DMARC checks.

Office 365 has a mechanism to address this:
https://learn.microsoft.com/en-us/office365/troubleshoot/antispam/sender-rewriting-scheme

But, this is really on the other provider. If they are dropping this, you need to talk to them to see if you can whitelist these messages

Answer 2

@Alain Sorrentini
Here is a summary about this thread, it may be useful to you to narrow down the related issue:

Question: When a customer send email to two mailboxes which hosted in different tenants(Mainly mailbox is set forward email to secondary mailbox), this customer will receive a NDR from secondary mailbox.

Solution: Using Outlook rule to forward email to another mailbox, the NDR message will only sent to the mainly mailbox rather than the customer mailbox. So, this issue is related with communication between the customer mailbox and secondary mailbox.

Suggestion: When you get the similar issue later, you can detect the communication between each mailbox separately, in this way, you will could narrow down and solve this question.